Switches presently used for this purpose typically comprise a pressure responsive snap acting disc member mounted in a housing with one face of the disc in fluid receiving communication with the fluid being monitored. The disc, upon snapping from one dished configuration to an opposite dished configuration, is adapted to transfer motion to a pin slidably disposed on the opposite face side of the disc. The pin extends between the disc and an elongated movable contact arm cantilever mounted in a switch chamber within the housing. A movable electrical contact is mounted on the movable contact arm at the distal free end thereof and is adapted to move into and out of engagement with a stationary contact mounted in the housing. The movable contact arm and the stationary contact arm are attached to respective terminals mounted in spaced apart relation on the housing as by riveting or welding.
Designs of the type described have inherent quality concerns due to the relatively large number of operations involved in manufacturing the switches such as pin gauging, pin length sizing, riveting and so on. Another limitation of the prior art switches relates to the type of switching mechanism employed. Once the disc has snapped causing the motion transfer pin to force the movable contact arm toward the stationary contact and into engagement with the stationary contact, the movable contact arm becomes, in effect, a simply supported beam and concomitantly the stresses in the movable contact arm become very high, relatively to the yield strength of the material used for the movable contact arm, generally beryllium copper (yield strength of approximately 140,000 psi).